Method of static mixing to produce metal foam

ABSTRACT

Ingredients required to make metal foam having particulate members such as glass beads or steel wires embedded therein are mixed in a static mixer having no moving parts.

United States Patent [191 Rock [ Nov. 20, 1973 METHOD OF STATIC MIXING TO PRODUCE METAL FOAM [75] Inventor: Edward J. Rock, Blue Mounds, Wis. [73] Assignee: ,Iohen lij orlrsten, M adis n Wis. [22] Filed: Feb. 4, 1972 [21] App]. No.: 223,547

[52] U.S. Cl 164/79, 164/133, 164/337, 75/20 F, 222/145, 259/180 [51] Int. Cl B2241 27/00 [58] Field of Search 75/20 F; 164/79, 164/133,337; 222/145; 259/180 [56] References Cited UNITED STATES PATENTS 2,983,597 5/1961 Elliott 164/79 2,930,767 3/1960 Novak 75/20 F 2,354,807 8/1944 Fox et al. 75/20 F 2,322,581 6/1943 Lytle 75/20 F 2,895,819 7/1959 Fiedler 75/20 F 3,055,763 9/1962 Kreigh 106/71 3,224,846 12/1965 Fiedler et al 29/1835 3,617,594 11/1971 Willy 264/45 OTHER PUBLICATIONS Fiber Metallurgy Steel, 10 Aug. 1959, pp. 126-128, Chemical Engineering, Pattison, May 19, 1969, p. 94.

Primary Examiner-J. Spencer Overholser Assistant Examiner-Vemon K. Rising Attorney-Johan Bjorksten [5 7 ABSTRACT Ingredients required to make metal foam having particulate members such as glass beads or steel wires embedded therein are mixed in a static mixer having no moving parts.

9 Claims, 4 Drawing Figures Patented Nov. 20, 1973 3,773,098

3 Sheets-Sheet l Patented Nov. 20, 1973 3,773,098

3 Sheets-Sheet 2 MOLTEN METAL'26 GRANULAR FOAMING AGENT-25 I FIBROUS PARTICLES'Z? V g Paiented Nov. 20, 1973 3 Sheets-Sheet 5 METHOD OF STATIC MIXING TO PRODUCE METAL FOAM This invention relates to processes for producing metal foam bodies.

SUMMARY Heretofore it has been regarded as necessary to'introduce a large amount of energy into the mixing of molten metal and foaming agent in order to provide a suitable mixture for the production of metal foam bodies. Thus, the use of high shear forces has been described in the Elliott U.S. Pat. No. 2,751,289 and the use of high intensity mixers, rotating at rapid rates for short periods of time, has been described in other references, e.g., Elliott U.S. Pat. No. 2,983,597.

In accordance with the present invention, foam metal and, more particularly, foam metal having high concentrations of particulate fibrous or non-fibrous material incorporated therein, may be prepared without need for such high energy inputs. In accordance with the present invention only very gentle mixing is necessary.

In accordance with the invention a mixer is used which contains no moving parts and consists in the most general case of a hollow tube having a plurality of baffles extending across the interior. Particularly suitable embodiments are described in the cited prior art references. A preferred embodiment comprises a hollow cylindrical tube provided with baffles, each of which is a flat sheet twisted through one-half turn with the axis of the twist lying on the axis of the tube. Each baffle member is installed with ts leading edge oriented at 90 to the trailing edge of the next previous baffle member.

Insuperable difficulties may be encountered in attempting to utilize such a mixing device in accordance with the descriptions of the prior art. Such descriptions call for introducing components to the mixing means by pumping or the like to entirely fill the mixing means.

In accordance with the invention, as a critical step, such a mixing device is operated partly empty as more fully described hereinafter to obviate difficulties encountered with such sharp particulate material as the foaming agent and with fibrous material such as steel or glass fibers which may be added.

OBJECTS It is therefore an object to provide an improved method for providing metal foam bodies.

Another object is an improved method for mixing ingredients for providing metal foam bodies.

Another object is an improved method for incorporating high proportions of high melting fibrous members in metal foam bodies.

Further objects will be apparent from the following detailed description.

DRAWINGS In the drawings like reference numerals refer to like parts and:

FIG. 1 is a schematic cross-sectional elevation of one embodiment;

FIG. 2 is a schematic cross-sectional elevation of another embodiment;

FIG. 3 is a schematic cross-sectional elevation of another embodiment;

FIG. 4 is a schematic cross-sectional elevation of another embodiment.

DESCRIPTION Referring now to FIG. 1 a mixing device indicated generally as 1 comprising hollow cylindrical tube 2 containing baffles 3 which, as shown, may be retained within tube 2 by any suitable means such as by use of an adhesive such as an epoxy resin, by furnace brazing, by sweating or the like. Each of baffles 3 may as shown consist of a flat piece of metal twisted through 180, that is, given turn of twist, with the axis of each being coincident with the axis of the tube. Other shapes of baffles may suitably be used.

In a preferred embodiment, molten eutectic alloy 5 of 65 percent aluminum and 35 percent magnesium is poured from crucible 6 into the top of mixer 1 and granular titanium hydride 7 in the ratio of 1 part of hydride to 10 parts of alloy is fed from vibratory feeder The flow rate of alloy and hydride is so adjusted in conjunction with the size of orifice 12 at the bottom of tube 2 that the liquid level 10 of the mixture 1 l of alloy and hydride within tube 2 is below the uppermost three of baffles 3, By suitable choice of flow rates and orifice size the liquid head above the orifice and consequently the liquid height may be maintained relatively stable. In this manner the first three stages of mixing of alloy and hydride take place in conjunction with baffles which are not submerged so that by the time the ingredients reach liquid level 10 the hydride is sufficiently wetted and dispersed that it does not flat on the surface of the alloy.

The mixture 11 thus produced may be fed to mixer l which may correspond to mixer l and may comprise tube 2' having orifice l2 and baffles 3' which may correspond to tube 2, orifice l2 and baffles 3. Into mixer 1' may also be fed molten metal 13, such as aluminum (in a preferred embodiment in the ratio of 9 parts to one part of mixture 11) from crucible l4. Fibrous particulate members 15 such as 28 gauge steel wires having an average length of 3/8 inches may be added to mixer 1 from vibratory feeder 16 in any suitable ratio such as 25 parts to parts of aluminum.

As with mixer 1, input flow rates to mixer 1' may be adjusted in conjunction with the size of orifice 12 to provide a relatively static head and therefore relatively stationary liquid level 22 which is preferably located below at least three of baffles 3.

In this manner, as a critically desirable step, molten materials 11 and 13 are mixed with fibers 15 in at least three stages provided by three of non-submerged baffies 3 prior to reaching liquid level 22 so that fibers 15 are sufficiently wetted and dispersed in molten metal prior to reaching liquid level 22 that they do not form birds-nests and do not float on the liquid surface.

The mixture 21 produced in mixer 1' may partially foam in the mixer.

Mixture 21 may be fed from orifice 12 to mold 23' wherein it may further foam and then may cool and solidify to form a molten metal body having the above described fibers incorporated therein.

In another embodiment, as shown in FIG. 2, a mixer indicated generally as 1" utilized in the process of the invention may correspond to mixer l with the exception that no orifice is provided at the bottom of tube 2" which otherwise corresponds to tube 2.

In operation, as shown, foaming agent 25, molten metal 26 and fibrous particles 27 may be added at such rates that tube 2" is never filled and none of baffles 3 therein are at any time entirely submerged and thus all possible problems with floating of either granular foaming agent or fibrous particles on a molten metal surface are entirely eliminated Mixture 29 thus produced may be introduced to mold 33 and may then foam, then cool and solidify therein to provide a suitable molten metal body having fibrous particles disposed therein.

Referring now to FIG. 3, a mixer 1 may be similar or identical to mixer 1" or mixer 1. As shown, no ori fice may be provided at its lower end or in certain instances an orifice such as orifice 12 may be provided. Mixer 1" is oriented slantwise as shown and is provided with baffles 3.

There may be introduced to the upper end of mixer 1' a stream of molten aluminum 34 from pump 35, a stream 36 of molten eutectic alloy of aluminum and magnesium having 12 percent zirconium hydride foaming agent incorporated therein from pump 37 and a stream of fibrous glass particles 38 from vibratory feeder 39.

The rates of introduction of the ingredients are preferably adjusted in relation to the pressure drop across baffles 3 such that an inclined liquid level 40 is provided and less than all, specifically at least 3 of bafiles 3 are not fully submerged, accordingly, the ingredients are sufficiently thoroughly mixed prior to reaching the area at which the baffles are entirely submerged that problems of separation of ingredients prior to undergoing initial mixing are obviated.

The mixture 41 thus produced may foam in part within mixer 1". Mixture 41, after passing through mixer 1", may be introduced into mold 43 wherein it may further foam and may then cool and solidify to provide a metal foam body as above described.

Referring now to FIG. 4, another embodiment is shown wherein a mixing device indicated generally as 51 comprises a tube 2" which corresponds to tube 2" except that it is conical. Baffles 3" therein may, if desired, correspond to baffles 3 except for being shaped to conform to the internal conical walls of tube 2".

Molten metal 54 from pump 55, molten eutectic alloy 56 from pump 57 and fibers 58 from vibratory feeder 59 may be introduced into the top of tube 2" at such rates that a relatively stationary liquid head and corresponding liquid level 60 is provided, leaving at least three of baffles 3" partially exposed and less than entirely submerged to obviate problems of one ingredient floating on the surface of another in such manner as to reduce mixing effectiveness. Foaming agent may be incorporated in alloy 56.

Mixture 62 flowing from mixer 51 may be introduced to mold 63 wherein it may foam and may then cool and solidify to provide a molten metal body as above described.

In accordance with the invention, one may operate either mixer 1", mixer 1 or mixer 51 in place of mixer 1 or mixer 1'. In other words the invention is not restricted to either the operation of two mixers in series as described in connection with FIG. 1 nor to the oper ation of only one mixer as described in conjunction with FIG. 2, 3 or 4.

The invention relates critically and particularly to the method of operating a mixer of the general type herein described in the manner herein described, namely, so that all or at least some and more particularly at least 3 of the baffle members are partially exposed or not completely submerged. Such operation may be facilitated by providing the mixer with an output orifice, by providing the mixer in conical form or by orienting the mixer slantwise. In any event, as described above, ingredients are mixed by flowing them over unsubmerged baffles either for a portion of their travel or for the entirety of their travel through the device.

The process of the invention is particularly applicable for particulate materials which cannot be pumped and especially applicable for mixing particulate materials with liquids in instances where the particulate materials are fibrous or sharp-cornered and not only cannot be pumped but are difficult to feed in any manner whatever and furthermore tend to birds-nest and tend to float on the surface of the liquid with which they are to be mixed. Such floating need not be by reason of being lighter in density than the liquid but may result from slowness in wetting whereby surface tension supports the particulate material.

Having thus described the invention, I claim:

1. In the process of making metal foam bodies having fibrous particles incorporated therein which includes mixing the ingredients molten metal, fibrous particles and foaming agent, the step of mixing said molten metal, fibrous particles and foaming agent by continuously introducing them into and through a baffled tube with at least three baffles therein such that the portion of the tube containing said at least three baffles is not entirely filled by said ingredients while they flow over said baffles.

2. The process of claim 1 wherein no part of said tube is entirely filled by said ingredients.

3. The process of claim 1 wherein a portion of said tube is entirely filled by said ingredients.

4. The process of claim 3 wherein said tube is oriented substantially vertically and the level in said tube is controlled in part with an orifice at the outlet of said tube.

5. The process of claim 3 wherein said tube is substantially conical.

6. The process of claim 3 wherein said tube is oriented slantwise.

7. The process of claim 6 wherein said tube is substantially conical.

8. The process of claim 6 wherein said tube is substantially cylindrical.

9. The process of claim 9 comprising the additional step of controlling in part the level in said tube with an orifice at the outlet thereof. 

1. In the process of making metal foam bodies having fibrous particles incorporated therein which includes mixing the ingredients molten metal, fibrous particles and foaming agent, the step of mixing said molten metal, fibrous particles and foaming agent by continuously introducing them into and through a baffled tube with at least three baffles therein such that the portion of the tube containing said at least three baffles is not entirely filled by said ingredients while they flow over said baffles.
 2. The process of claim 1 wherein no part of said tube is entirely filled by said ingredients.
 3. The process of claim 1 wherein a portion of said tube is entirely filled by said ingredients.
 4. The process of claim 3 wherein said tube is oriented substantially vertically and the level in said tube is controlled in part with an orifice at the outlet of said tube.
 5. The process of claim 3 wherein said tube is substantially conical.
 6. The process of claim 3 wherein said tube is oriented slantwise.
 7. The process of claim 6 wherein said tube is substantially conical.
 8. The process of claim 6 wherein said tube is substantially cylindrical.
 9. The process of claim 9 comprising the additional step of controlling in part the level in said tube with an orifice at the outlet thereof. 